High density and high integration semiconductor devices have been manufactured and supplied, owing to a development of fine technology in a semiconductor manufacturing. Particularly in a semiconductor memory manufactured in a sub micron rule, a great number of memory elements are formed in one chip, which allows recording music and video for a long time, coupled with a lowered bit unit price and with a development in data compressing technology. Furthermore, employing an organic semiconductor element with a lower price may make the bit unit price lower.
In the semiconductor memory useful as a record medium, as well as in view of the cost, it is expected to prevent or block the data reading after a predetermined time elapse from the data recording, for example in an application for a commuter pass (ticket), or an application in a rental business of music or video soft and the like.
As the semiconductor memory compatible to such an expectation, Japanese Patent Application Laid-Open No. H10-189780 discloses an example of the technology. According to this, a gate insulation layer may be formed of a first layer of a silicon dioxide film, a second layer of a silicon nitride film and a third layer of a silicon dioxide film, in which a composition rate of Si atom and N atom in the second layer of the silicon nitride film is set to a value corresponding to a desired data effective time. Owing to this construction, the data effective time is expected to be set in such a manner that a shallow electric charge lap is positively formed to deteriorate the memory retention, and an amount of the electric charge to be accumulated in an electric charge accumulation mechanism is reduced and thereby the lifetime of the data retention is shortened. The lifetime of record data in this type of memory is determined by controlling the composition rate of Si atom and N atom in the silicon nitride during the chip fabrication.